Abstract: A working cannula for arthroscopy, in particular of the shoulder and the knee, comprising a tube and a removable closure pin member (trocar) which is guided in the tube, wherein the tube has an external screwthread which is continued by a screwthread of the tip, which projects beyond the tube, of the closure pin member. The closure pin member has a central bore extending therethrough, for receiving a guide wire. The closure pin member locks on to the tube so that when the closure pin is rotated, the tube rotates to facilitate anchoring of the screwthread into a patient.